1. Field of the Invention
The present invention relates to a variable damping valve of a shock absorber, and more particularly, to a shock absorber mounted with a variable damping valve capable of properly adjusting a damping force according to road conditions, travel conditions and the like while a vehicle is traveling, thereby improving ride comfort and control stability.
2. Description of the Related Art
A shock absorber of a suspension system mounted in a vehicle is a vibration-proof and shock-absorbing apparatus installed between an axle and a vehicle body to improve ride comfort by absorbing a vibration or shock transmitted from a road to the axle when the vehicle travels. The interior of the shock absorber is filled with oil and/or gas.
Shock absorbers include a variable damping shock absorber adapted to properly adjust a damping characteristic according to road and travel conditions so as to improve ride comfort or control stability. The variable damping shock absorber has a configuration in which a variable damping valve for adjusting a damping force is provided at a side surface of an outer tube of a conventional shock absorber.
Conventional variable damping valves are classified into a normal type variable valve and a reverse type variable valve according to methods of controlling a damping force in response to the movement of a vehicle. The reverse type variable valve is characterized in that compression and extension strokes are controlled by an additional valve in response to the movement of a vehicle. Thus, in the reverse type variable valve, a weak damping force is generated during the extension stroke and a strong damping force is generated during the compression stroke, or a strong damping force is generated during the extension stroke and a weak damping force is generated during the compression stroke. However, since the reverse type variable valve employs such an additional valve, there are disadvantages in that production costs thereof increase and the use of the additional valve results in a relatively larger size and deteriorated mountability.
In the normal type variable valve, a single valve is used to control damping forces during both the compression and extension strokes. Thus, in the normal type variable valve, strong damping forces or weak damping forces are generated during both the compression and extension strokes.
A conventional reverse type variable valve is disclosed in Korean Patent Application No. 1997-58101 entitled “Damping force-adjustable hydraulic shock absorber,” wherein a damping force generating valve 11 is connected to a side of a variable damping shock absorber 1. The damping force generating valve will be described with reference to FIG. 1.
Since compression-side and extension-side valve mechanisms of the damping force generating valve 11 have the substantially same structure, an enlarged view common to them is shown in FIG. 2.
As shown in the figures, the damping force generating valve 11 is constructed in such a manner that two bottomed cylindrical valve bodies 13 and 14 are fitted into a bottomed cylindrical case 12, a proportional solenoid actuator 15 (hereinafter, referred to as “actuator 15”) is mounted in an opening of the case 12, and the interior of the case 12 is partitioned into three fluid chambers 12a, 12b and 12c by the valve bodies 13 and 14.
Annular sealing members 16 and 17 are fitted into openings of the valve bodies 13 and 14, respectively, and a cylindrical guide member 18 threadly coupled to the actuator 15 penetrates through the valve bodies 13 and 14 and the sealing members 16 and 17 and is then secured by a nut 19. A sidewall of the case 12 is provided with connection holes 20, 21 and 22 communicating respectively with the fluid chamber 12a, 12b and 12c. The connection holes 20, 21 and 22 are connected to a cylinder through flow passages of the shock absorber, respectively.
A plurality of circumferentially arranged flow passages 26 and 27 (inlet passages) (only two flow passages are shown in FIG. 1) are formed at lower portions of the valve bodies 13 and 14 to axially penetrate through the valve bodies, respectively. Further, on an inner wall at the lower portion of each of the valve bodies 13 and 14, an annular inner sealing part 28 or 29 (see FIG. 2) is provided to protrude at an inner peripheral side of the passage 26 or 27, an annular valve seat 30 or 31 (see FIG. 2) is provided to protrude at an outer peripheral side of the passage 26 or 27, and an annular outer sealing part 32 or 33 (see FIG. 2) is provided outside the annular valve seat 30 or 31 and in the vicinity of a sidewall of the valve body 13 or 14. Annular grooves 34 and 35 are formed between the valve seats 30 and 31 and the outer sealing parts 32 and 33, respectively. The grooves 34 and 35 communicate with the fluid chambers (as at 12b and 12c in FIG. 1) through flow passages 36 and 37 (outlet passages), respectively.
As shown in FIG. 2, a disk-shaped orifice plate 38 or 39, which will be described later, and a spacer 40 or 41 are stacked on the inner sealing part 36 or 37 of each of the valve bodies 13 and 14. A disk valve 42 or 43 is stacked thereon; a retainer disk 44 or 45 with a diameter slightly smaller than that of the disk valve 42 or 43 is additionally stacked thereon; a plurality of disk-shaped leaf springs 46 or 47 (spring means) (only three leaf springs are shown in the figure) with a diameter smaller than that of the retainer disk 44 or 45, and a spacer 48 or 49 are further stacked thereon; and an outer periphery of the disk valve 42 or 43 is placed on the valve seat 30 or 31.
A flexible sealing ring 50 or 51 is fitted into the valve body 13 or 14. An inner periphery of the flexible sealing ring comes into contact with an outer periphery of the retainer disk 44 or 45 while slightly overlapping with each other, and an outer periphery of the flexible sealing ring comes into contact with the outer sealing part 32 or 33. A retainer ring 52 or 53 comes into contact with the top of the outer periphery of the flexible sealing ring 50 or 51, and an outer periphery of an annular sealing spring 54 or 55 comes into contact with the top of the retainer ring. The sealing member 16 or 17 fitted into the valve body 13 or 14 is in contact with the inner peripheries of the spacer 48 or 49 and the sealing spring 54 or 55, and secures the inner peripheries of the disk valve 42 or 43, the retainer disks 44 or 45 and the leaf springs 46 or 47 to the inner sealing part 28 or 29 and simultaneously secures the outer periphery of the sealing ring 50 or 51 to the outer sealing part 32 or 33.
The sealing member 16 or 17, the retainer disk 44 or 45, and the sealing ring 50 or 51 define a pilot chamber 56 or 57 at the rear of the disk valve 42 or 43 within the valve body 13 or 14. At this time, the sealing spring 54 or 55 seals a gap between the valve body 13 or 14 and the sealing member 16 or 17. Further, to securely seal a contact portion of the retainer disk 44 or 45 and the sealing ring 50 or 51, the sealing ring 50 or 51 is assembled in such a manner that the outer periphery thereof is at a level slightly lower than that of the inner periphery thereof with respect to the bottom of the valve body 13 or 14, thereby pressing down the retainer disk 44 or 45. In the figures, reference numerals 58, 59, 60, 61 and 62 designate O-rings.
A sidewall of the guide member 18 is provided with ports 63 and 64 communicating respectively with the pilot chambers 56 and 57, and ports 65 and 66 communicating respectively with the fluid chambers 12b and 12c. The orifice plate 38 or 39 mounted on the inner sealing part 28 or 29 is provided with fixed orifices 67 or 68. An upstream passage is constructed by the fixed orifices 67 or 68, a cut-away portion 69 or 70 of the inner sealing part and a groove 71 or 72 of an outer periphery of the guide member 18. With the upstream passage, the flow passage 26 or 27, and the port 63 or 64, i.e., pilot chamber 56 or 57, communicate with each other. A spool 73 is slidably fitted into the guide member 18 to adjust the area of the flow passage (downstream passage) between the port 63 or 65 and the port 64 or 66. The spool 73 is urged (forced) toward the actuator 15 by a compression spring 74 and is moved against the pressing force of the spring 74 by an actuating rod 75 of the actuator 15, so that the areas of flow passages of the port 63 and the port 66 (variable orifice) can be adjusted.
However, in such a conventional structure, the respective pilot chambers 56 and 57 formed at the rears of the disk valves 42 and 43 within the valve bodies 13 and 14 by being partitioned by the sealing members 16 and 17, the retainer disks 44 and 45, and the sealing rings 50 and 51 have a very complicated structure in which the sealing rings 50 and 51 are fixed by the retainers 52 and 53 placed thereon. If the retainers 52 and 53 have uneven top and bottom surfaces, unbalance occurs in the pressing forces of the retainers 50 and 51. This causes a problem in that pressure in the pilot chambers 56 and 57 becomes unstable, resulting in dispersion of a damping force. That is, the occurrence of the dispersion in the pilot chambers 56 and 57 greatly deteriorates the performance of the shock absorber.